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Abstract
The Neotropical invasive plant Chromolaena odorata R.M. King and H. Robinson (Asteraceae) is a serious weed in West and Central Africa and two biological control agents that have been introduced into West Africa to help reduce its impacts on agriculture and biodiversity, have established. The stem-galling fly, Cecidochares connexa (Macquart) (Diptera: Tephritidae), has spread widely across West Africa since its release in only Côte d’Ivoire, occurring in six countries. This study aimed to investigate whether the gall fly had spread further across West Africa and into Central Africa. Here, we surveyed C. odorata for C. connexa galls in Cameroon between October 2018 and October 2020, along roadsides, on farms, residential areas, and abandoned plots, encompassing various vegetation types. Additional surveys were conducted across four countries (Ghana, Togo, Benin Republic and Nigeria) in West Africa that we considered the probable pathway for the spread of the gall fly into Central Africa. Cecidochares connexa was present at five of the six locations surveyed in Cameroon, albeit in varying abundance. In Africa, these findings represent the first-ever report of C. connexa outside of West Africa. In West Africa, we recorded significant expansion in the geographic range of C. connexa, as reflected in the absent-present record of C. connexa in two locations in Nigeria and one in Ghana, as well as its occurrence in all locations surveyed in Benin Republic and Togo. Clearly, Ghana, Togo, Benin Republic and Nigeria served as the dispersal pathway of C. connexa from the release sites in Côte d’Ivoire into Cameroon, covering over 2,300 km. Following the spread and establishment of C. connexa into Cameroon, we anticipate that it will continue to spread further into other parts of Central Africa which are climatically suitable. Cecidochares connexa is currently the only biological control agent for C. odorata in Central Africa. Given that it has significantly reduced populations of C. odorata in other countries where it has established, it is expected to have a similar impact in Central Africa.
Highlights
Novel environments have increasingly become susceptible to biological invasions due to human-mediated activities, encompassing movement, global trade, and climate change, and there is no apparent indication of this abating [1,2,3,4]
Chromolaena odorata occurring in both fragmented patches and clutched densities were surveyed across 35 study locations in West Africa and Cameroon for the presence of C. connexa between October 2018 to October 2020
C. odorata occurs in all Central African countries except São Tomeand Prıncipe [21,22,23] (Fig 1), the surveying of C. connexa in the region was restricted to Cameroon because the country borders Nigeria and is considered the potential entry point into Central Africa
Summary
Novel environments have increasingly become susceptible to biological invasions due to human-mediated activities, encompassing movement, global trade, and climate change, and there is no apparent indication of this abating [1,2,3,4]. These scenarios are exemplified by the perennial scrambling invasive alien plant Chromolaena odorata R.M. King and H. The founder population of C. odorata, which is believed to have been introduced accidentally into Nigeria through an imported consignment from Sri Lanka in the late 1930s [7], successfully established and quickly became pervasive across West and Central Africa, with devastating impacts on biodiversity and agriculture [5]. Chromolaena odorata is still spreading and is present in 12 of the 16 countries in West Africa, following the recent report of its occurrence in Guinea-Bissau [8], and it has been reported in seven of the eight countries in Central Africa [6, 9]
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